Belt driven continuously variable transmission

ABSTRACT

This invention relates to a belt driven continuously variable transmission having a pressure regulating cam mechanism giving an axial force corresponding to the transmission torque to a pulley and preventing too much belt pressing force. A retainer is fixed on a boss section of a stationary sheave and a spring made of multiple disc springs is situated on the outer surface of a boss section of a movable sheave for contact the retainer. A spring apparatus is composed of the retainer and the spring. Accordingly, at the decelerating range with large shifting ratio, besides the axial force made by the pressure regulating cam mechanism, the spring apparatus generates pressing force by contacting the retainer and maintains the belt holding force. When the shifting ratio is small, the spring returns to its natural length and disengages from the retainer.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a belt driven continuously variabletransmission and especially relates to a belt driven continuouslyvariable transmission suitable for using in an automatic variabletransmission to be mounted on an automobile more particularly, itrelates to a pressure regulating mechanism section generating a axialforce to correspond to a transmission torque.

2. Description of the Prior Art

Generally, this V-belt type continuously variable transmission (CVT) hasa primary pulley and a second pulley each of which is made up of amovable sheave and a stationary sheave. Metallic belt is wound aroundboth of these pulleys. A transmission shift done at a required moment bymoving the movable sheave with a hydraulic piston.

Therefore, the continuously variable transmission, where a hydraulicpressure is used, needs an oil pump and a hydraulic pressure passage.This structure makes the device not only large and complicated but alsounfavorable for the transmission efficiency and for the belt endurancebecause the structure requires the belt holding force more than needed,which furthermore, makes it impossible to transmit due to belt holdingforce becoming short in supply when the hydraulic pressure decreasessome reason.

The applicant of the present invention has proposed that a belt drivencontinuously variable transmission 30', as shown in FIG. 13, having ametallic belt 33 around a primary pulley 31 and a secondary pulley 32,whose movable sheave 31b and 32b are moved axially by actuatormechanisms 35 and 36 such as ball thread mechanism, and to arrange apressure regulating cam mechanism 34' imparting an axial force whichcorresponds to a transmission torque to a fixed sheave 31a. (refer tothe Japanese Laid Open Patent No. 62-13853).

By the pressure regulating mechanism 34', this belt driven continuouslyvariable transmission 30' gets the belt pushing force which is inproportion to the transmission torque, however, with reference to theshifting ratio only a constant belt holding force can be obtained.

While, in the continuously variable transmission the belt holding forcevaries by the shifting ratio, and when the shifting ratio gets small therequired belt holding force gradually decreases even at the full openingof the throttle.

However, the continuously variable transmission 30' has the pressureregulating cam mechanism 34+ to generate a constant holding forceaccording to the lowest speed shifting which requires the largestholding force. So at the lower speed shifting state of frequent use, alarge belt holding force works. As result, a load much more thannecessary works on the V-belt, the bearing and the pressure regulatingcam mechanism, and causes decadance of transmission ratio, andmaintenance and noise troubles.

This invention has as its purpose provision of a belt drivencontinuously variable transmission which is designed to have adequatebelt holding force by varying axial force working on pulleys accordingto speed shifting ratio.

SUMMARY OF THE INVENTION

This invention includes, as shown in FIG. 1 for example, a belt drivencontinuously variable transmission (30) with a primary pulley (31) and asecondary pulley (32) both of which are supported respectively by ashaft (30b) and (30a) both of which are composed of two sheaves (31a),(31b), (32a) and (32b) all relatively movable in the axial direction anda belt (33) which is wound around the pulleys (31) and (32). This beltdriven continuously variable transmission (30) also has a pressureregulating mechanism (34) such as a cam mechanism giving a axial forcecorresponding to the transmission torque to both or either of thepulleys (31) and (32) and also has actuator mechanisms (35) and (36)such as a ball thread mechanism to move movable sheaves (31b) and (32b)axially.

This invention adopts a spring means (1) which works on at least onepulley (31), and which reduces pressing force according to decrease ofshift ratio.

With the above structure, the rotation of the input member (90C) istransmitted to the fixed side race (34a) of the pressure regulatingmechanism (34) and the fixed sheave (31a) of the primary pulley (31)through the pressure regulating mechanism (34). By this, an axial forcecorresponding to the transmission torque works on the sheave (31a).Furthermore, the torque transmitted to the primary pulley (31) istransmitted through the belt (33) to the secondary pulley (32) and thento the secondary shaft (30a). Both pulleys (31) and (32), whoseeffective diameters are adjusted at the required moment by the actuatormechanisms (35) and (36), are shifted steplessly and variably. At thedecelerating condition U/D (underdrive), for example, (refer to theupper part of the FIG. 1) the spring means (1) gives a pressing force asto hold the belt (33) to the fixed sheave (31a) and the movable sheave(31b). This belt holding force becomes largest at the lowest shiftingcondition; the spring means (1) returns to the original length as theshifting ratio becomes small. The belt holding force is supported by notonly the pressure regulating mechanism (34) but also spring means (1),so that the axial force generated by the pressure regulating mechanism(34) is decreased.

This invention, as has been explained up to now, arranges the springmeans (1) and (1)' whose pressing force decrease as the shifting ratiodecreases. The spring means (1), (1') secures necessary axial forcetogether with the axial force generated by the pressure regulatedmechanism (34), so that the pressure regulating mechanism (34) can bemade to generate smaller axial force. Therefore, at all the ranges ofthe shifting ratio, especially smaller shifting ratio of the mostfrequent use, the belt holding force decreases so that the load of thethrust bearings (3a) and (3b) which support the axial force of thepulley (31) decreases. Because the pressure regulating mechanism (34)which generates small axial force can be used, improvements are achievedin the maintenance of the belt driven continuously variable transmissionand of the belt itself by decreasing the belt holding force working onthe belt (33). Also the transmission efficiency of the continuouslyvariable transmission is improved. Furthermore, noises emitted by thebelt on the pulley (31) can be reduced so that the reliability of thebelt driven continuously variable transmission (30) can be improved.

As the spring means (1), if the disc spring (1b) working only at largershifting ratio is employed, simple as the structure is, the spring meanscan work usefully at the decelerating range which needs a large beltholding force.

If the spring means is a combination of plural springs which havedifferent pressing forces and natural lengths such as the disc spring(1'b) and the coil spring (1c), the belt pressing force varies accordingto the shifting ratio, and the degrees of freedom for the design onnecessary belt pressing force can be increased.

Incidentally, the reference numerals in the parentheses are used onlyfor reference to the drawings and do not define the invention. The samenumber may be used differently in the following description than in theprevious description in which broader concepts are adopted.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a cross sectional view of a belt driven continuously variabletransmission relating to this invention;

FIG. 2 is a schematic representation of a continuously variabletransmission where this invention is applicable;

FIG. 3 is a table of operation of each element;

FIG. 4 is a cross sectional view of the continuously variabletransmission;

FIG. 5 is a graphical representation of the axial force of a pressureregulating cam mechanism vs. the shifting ratio;

FIG. 6 is a graphical representation of the belt pressing force vs. theshifting ratio;

FIG. 7 and FIG. 8 are graphical representations of the axial force of apressure regulating cam mechanism vs. torque;

FIG. 9 and FIG. 10 are graphical representations of the belt pressingforce vs. torque;

FIG. 11 is a cross sectional view of a primary pulley of an embodimentpartly modified;

FIG. 12 is a graphical representation of a belt pressing force vs.ratio;

FIG. 13 is a cross sectional view of the prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A detailed description of the preferred embodiments shall now be shown.

This automatic continuously variable transmission 12, as shown in FIG. 1has a single planetary gear device 20, a belt driven continuouslyvariable transmisson 30, a transfer device 80, an input shaft 60, anoutput member 70 composed of a reduction gear device 71 and adifferential device 72, a fluid coupling 13 having a lock-up clutch CLand a forward/reverse switching device 90 composed of a dual planetarygear device. And in the single planetary gear device 20, an element 20S(or 20R) to be a reaction force supporting member when using the singleplanetary gear device 20 as a reduction mechanism moves together with arestraining means F and B1 through a transfer device 80, and connects ordisconnects with the input shaft 60 through a high clutch C2.

To put it concretely, the ring gear 20R of the planetary gear device 20moves together with a secondary shaft 30a of the continuouslytransmission 30, a carrier 20C moves together with the output member 70,and the sun gear 20S moves together with a low one-way clutch F and alow coast & reverse brake B1 composing a restraining means through thetransfer device 80 and also moves together with the high clutch C2.

In the dual planetary gear device 90, a sun gear 90S connects to theinput shaft 60, a carrier 90c connects to both the primary shaft 30b ofthe continuously variable transmission 30 and the input shaft 60 throughthe forward clutch C1 and the ring gear 90R connects to the reversebrake B2.

Based on the above structure, each clutch, brake and one-way clutch inthe automatic continuously variable transmission 12 operate rate asshown in FIG. 3. shows that the lock-up clutch CL can move at a requiredmoment .

In detail, at the low speed side L of D range, the forward clutch C1connects and the low one-way clutch F operates. At this stage, therotation of the engine crank shaft is transmitted to the input shaft 60through the lock-up clutch CL or the fluid coupling 13, to the sun gear90S of the dual planetary gear device 90 directly and to the carrier 90Cthrough the forward clutch C1. Therefore, the dual planetary gearmechanism 90 rotates together with the input shaft 60 and transmits thepositive rotation to the primary shaft 30b of the belt drivencontinuously variable transmission 30. Furthermore, the rotation shiftedat a required moment at the continuously variable transmission 30 istransmitted from the secondary shaft 30a to the ring gear 20R of thesingle planetary gear device 20. While, at this state, the sun gear 20Swhich is the reaction force supporting element to receive the reactionforce is stopped by the low one-way clutch F through the transfer device80. So the rotation of the ring gear 20R is taken out from the carrier20C as a reduced rotation and transmitted to the axle 73 through thereduction gear device 71 and the differential device 72.

At the high speed side H of D range, not only the forward clutch C1 butalso the high clutch C2 connects. At this state, the positive rotationshifted at a required moment at the continuously variable transmissionis taken out from the secondary shaft 30a and input into the ring gear20R of the single planetary gear. While, at the same time, the rotationof the input shaft 60 is transmitted to the sun gear 20S of the singleplanetary gear device through the high clutch C2 and the transfer device80. By this process, torque of the ring gear 20R and the sun gear 20S iscombined and taken out from the carrier 20C. At this state, as therotation against the reaction force through the transfer device 80 istransmitted to the sun gear 20S, the torque circulation does not occurand the certain positive torque is transmitted through the transferdevice 80. The combined torque from the carrier 20C is transmitted tothe axle shaft 73 through the reduction gear device 71 and thedifferential device 72.

At the operation of D range, the rotation is free at the reverse torqueoperation (at the engine brake) based on the one-way clutch F, while atthe operation of S range, besides the low one-way clutch F, the lowcoast & reverse brake B1 operates and power can be transmitted even atthe reverse operation.

At the R range the reverse brake B2 operates together with the low coast& reverse brake B1. At this state, the rotation of the input shaft 60 isinput to the belt driven continuously variable transmission 30 as areverse rotation from the carrier 90C as the ring gear 90R of the dualplanetary gear device 90 is stopped. While, based on the operation ofthe low coast & reverse brake B1, the sun gear 20S of the singleplanetary gear device 20 is stopped so that the reverse rotation of theautomatic continuously variable transmission 30 is decelerated at theplanetary gear device 20 and taken out to the output member 70.

And at P range and N range, the low coast & reverse brake B1 operate.

The embodiment of the automatic continuously variable transmissionrealized will be shown along with FIG. 4.

This continuously variable transmission 12 has the transmission case 15where the input shaft 60 and the primary shaft 30b of the continuouslyvariable transmission 30 are supported on the same (first) shaft withrotation free. The secondary shaft 30a of the continuously variabletransmission device 30 and the gear axis 70a are supported on the sameshaft with rotation free and compose a secondary shaft. Furthermore, onthe primary shaft, are arranged, the fluid coupling 13 having thelock-up clutch CL, the forward clutch C1, the high clutch C2, the lowcoast & reverse brake B1, the reverse brake B2, a controlling section 40consisting of a low one-way clutch F, the dual plane-tary gear device 90composing the forward/reverse switching device and a hydraulic pressurepump 17. On the secondary shaft, the single planetary gear device 20 isarranged.

Furthermore, to explain the controlling section 40 and the inputsection, the input shaft 60 has one side edge which engages with thelock-up clutch CL and the output member of the fluid coupling 13 andanother side edge which engages with the sun gear 90S of the dualplanetary gear device 90. On the input shaft 60 a sleeve section 15awhich is fixed on the case 15 is arranged. To the sleeve section 15a, asprocket 81 is connected through the one-way clutch F, while a sleeveshaft 41 connecting to the input shaft 60 is supported with rotationfree. Furthermore, at one side of a flange section 41a extending fromthe sleeve shaft 41, the forward clutch C1 is arranged together with ahydraulic pressure actuator 42, and at the other side, the high clutchC2 is arranged together with a hydraulic pressure actuator 43. Theoperated side of the high clutch C2 is connected to the boss sectionwhich is connected to the low coast & reverse brake B1 arranged togetherwith a hydraulic actuator 45 in the case 15. The operated side of theforward clutch C1 is connected to the carrier 90C of the dual planetarygear device 90 whose ring gear 90R engages with the reverse brake B2arranged in the case 15 together with a hydraulic actuator 46 (referenceto FIG. 2). Here, the carrier 90C supports pinions 90P1 and 90P2, bothpinions mesh each other, the pinion 90P1 meshes with the sun gear 90S,the pinion 90P2 meshes with the ring gear 90R.

The single planetary gear device 20, whose ring gear 20R connects to theflange section `q` on the secondary shaft 30a of the belt drivencontinuously variable transmission 30 to be mentioned later on, isarranged on the gear shaft (output shaft) 70a also composing thesecondary shaft. On the gear shaft 70a, a sprocket 82 is supportedrotation free together with the sun gear 20S. On the gear shaft 70a, thecarrier 20C supporting the pinion 20P is spline-coupled.

While, between the sprocket 82 integral with the sun gear 20S and thesprocket 81 supported by the low one-way clutch F, a silent chain 83 iswound round and composes the transfer device 80 by these sprockets andthe chain.

The gear shaft 70a composes the output member 70 integrally with a gear71a, which engages with a gear 71c fixed on an intermediate shaft 71b.Furthermore, on the intermediate shaft 71b, a small gear 71d is formed.The small gear 71d engages with a ring gear 72a fixed on thedifferential device 72 and composes the reduction device 71. Theright/left front axle shaft 731 and 73r extend from the differentialdevice 72.

The belt driven continuously variable transmission 30 of this invention,as shown in FIG. 1, is arranged with the primary pulley 31, themsecondary pulley 32 and the belt 33 wound around both of these pulleys,which are made of stationary sheaves 31a, 32a and movable sheaves 31b,32b.

The stationary sheave 31a of the primary pulley 31 covers the primaryshaft 30b and has a long boss section `b` elongated to the side of themovable sheave 31b. A cylinder-shaped hub `a` is integrally formed onthe back surface of the flange section `d`. The outer diameter surfaceof the hub `a`, whose inner side control pressure regulating cammechanism 34 is supported by the case 15 with free rotation through aroller bearing 5e. The pressure regulating cam mechanism 34 is composedof a fixed race 34a and a movable race 34c, both of which havewave-shaped end surfaces and a roller 34b interposed between bothwave-shaped ends. The fixed race 34a is spline-coupled with the edge ofthe primary shaft 30b and stopped by snap rings. The movable race 34cconnects to a spline `a₁ ` arranged on the inner surface of the hubsection `a` with axial direction movement free. Between the fixed race34a and the inner surface of the hub section `a` certain interval `c` isarranged. Between the movable race 34c and the primary shaft 30b acertain interval `c` is also arranged. Therefore between the fixed race34a and the stationary sheave 31a, and, between the the movable race 34cand the shaft 30b, no torque is transmitted by frictional contact. Onthe outer diameter surface of the fixed race 34a, a spline is formed andthe input member, or the carrier 90C of the dual planetary gear 90 isspline-coupled. The movable race 34c transmits the torque to thestationary sheave 31a through the spline a₁, and produces the axialforce, which is in proportion to the transmitting torque, through manydisc springs 38 which are arranged in the concave section and whichproduce the preload.

The axial force based on the pressure regulating cam mechanism 34 asshown in FIG. 5, keeps a constant level regarding the shifting ratio. Inthis invention, the axial force (full line) is set lower by a certainamount than the prior art (chain line).

While, an oil passage `g` whose end is pluged by a cap `f` runs throughright in the middle of the primary shaft 30b where many side holessupplying lubricating oil to required places are formed. The base endportion, or the dual planetary gear device 90 side forms an "in-low"section `h` engaging with the input shaft 60. The outer diameter surfaceof the base end forms a screw section `i` and the section which engageswith the boss section `b` of the stationary sheave 31a is an oil groove`j`. The end of the shaft 30b, which is opposite the gear device 90,enlarges to form integrally a large diameter flange section `k`, whoseinner surface forms a seat for the thrust bearing 3a. While the 15 a cap15a is fixed by a bolt B covering the large diameter flange `k`. Theshoulder section 15b of the case 15 supports the regulating retainer 4.

The regulating retainer 4 is made of circular members having channelshape cross section. An inner diameter brim section 4a supports thestationary sheave 31a with rotation free by the inner surface of thebrim 4a through the radial roller bearing 5a. A spline `m` is formed onthe outer surface of the regulating retainer 4. The thrust bearing 3a issupported by the outside wall section 4b. A worm wheel 4c is formed onthe outer brim section of the outside wall section 4b. This worm wheel4c meshes with a worm 4d, and by rotating the worm 4d, the regulatingretainer 4 is rotated at the axially unvariable position in contact withthe bearing 3a.

Between the boss section `b` of the stationary sheave 31a and the bosssection `n` of the movable sheave 31b, a spring means 1 is arranged. Thespring means 1 is composed of a retainer 1a fixed on the boss section`b` of the stationary sheave 31a by a snap ring and a multiple discspring 1b arranged between the shoulder and the snap ring both of whichare on the outer surface of the boss section `n` of the movable sheave31b. When the effective diameter of the pulley 31 is small, or at thedecelarating condition (reference to the upper part of FIG. 1), theretainer 1a contacts with the disc spring 1b to give the pulley an axialforce to hold the belt. This axial force decreases as the effectivediameter, of the pulley 31 gets larger to allow the disc spring 1b toextend back to the natural length. And when the pulley 31 be-comeslarger than a certain value (reference to the lower part of FIG. 1), theretainer 1a and the disc spring 1b disengage and do not provide an axialforce.

While, at the movable sheave 31b the boss section `n` is supported bythe boss section `b` of the stationary sheave 31a with only slidemovement free through the ball spline 6a, and a ball thread device 35 isarranged on the back section of the flange section `o`. The ball threaddevice 35 is made of a bolt section 35a and a nut section 35b. On theinner surface of the bolt section 35a, a groove engaging with the spline`m` of the regulating retainer 4 is formed. On the outer surface of thenut section 35b a spline `e` is formed. A circular gear section 35cwhose circumferential section is formed into a wide circular gear isspline-coupled to the spline `e`. Between the gear section 35c and theflange section `o` of the movable sheave 31b, a thrust bearing 3b isinterposed. Therefore, a bolt section 35a of a ball thread device 35 isconnected without rotation to the case 15 through the regulatingretainer 4 and is connected to the primary shaft 30b through the thrustbearing 3a without axial movement. The nut section 35b of the ballthread device 35 is connected to the movable sheave 31b through thethrust bearing 3b so that the nut section 35b and the sheave 31b movetogether.

The secondary pulley 32 has a fixed sheave 32a and a movable sheave 32b.The fixed sheave 32a is supported by a roller bearing 5b in the case 15with rotation free and connected to a secondary shaft 30b withoutrotation through a key 6c. The movable sheave 32b is supported, withonly sliding movement allowed, on the secondary shaft 30a through a ballspline 6b.

The oil passage g' run through the middle of the secondary shaft 30a andhas the end pluged by a cap f'. Many side holes to supply lubricatingoil to required places are also formed in the secondary shaft 30a, whosebase end, or the side of the single planetary gear device 20, enlargesto be a large diameter flange section `q`. The diameter of the oilpassage hole g' becomes stair-shapedly large, corresponding to theflange section `q`. The section `q` is mounted on the output shaft 70athrough a needle bearing 5c. On the outer diameter of the shaft 30a,starting from the flange section `q`, a ball groove `r`, a key groove`s` and a screw `t` are formed in this order and each of them supportsthe movable sheave 32b and the stationary sheave 32a. A nut member 9 isscrewed to the screw `t`.

A regulating ring 7 is fixed by a bolt B on the approximately same planewith the needle bearing 5c of the case 15. Furthermore, a regulatingretainer 8 is supported by a shoulder section formed in the case 15. Theregulating retainer 8 whose cross section is channel shape, whose innerdiameter brim section 8a supports the secondary shaft 30a with rotationfree through the roller bearing 5d, and whose outer surface forms aspline `u`, is a circular shaped member. Furthermore, between theoutside of a side wall section 8b and the flange `q`, the thrust bearing3c is held and a gear 8c selectively engaging with a gear 7a of the ring7 is formed.

Furthermore, on the back side of a flange section `y` of the movablesheave 32b a ball thread device 36 which is composed of a bolt section36a and a nut section 36b is arranged. A groove mating with a spline `u`of the regulating retainer 8 is formed on the inner surface of the boltsection 36a. The, nut section 36b has a spline `x` formed on its outersurface, which is a non-circular gear sections 36c is spline-coupled.Between the gear section 36c and the flange section `y` a thrust bearing3d is interposed. So the bolt section 36a of the ball thread device 36is connected to the case 15 without rotation and to the flange section`q` of the secondary shaft 30a with no axial movement allowed throughthe thrust bearing 3c. The nut section 36b is connected to the movablesheave 32b, through the thrust bearing 3d, to axially move with themovable sheave 32b.

A shifting device 100 regulating the distance between the primary pulley31 and the secondary pulley 32 is placed between two pulleys 31 and 32so that each pulley and the device 100 form the apexes of triangle. Theshifting device 100, as shown in FIG. 4, has an operating shaft 101supported by the case 15 with rotation free. As FIG. 4 is a development,the operating shaft 101 is drawn at the upper part, however,practically, the operating shaft 101 is placed between the primary shaft30b and the secondary shaft 30a by an elevation. At the operating shaft101, a circular gear 102 and a non-circular gear 103 are fixed. Thenon-circular gear 102 engages with the non-circular gear 35c fixed tothe nut section 35b at the side of the primary pulley 31. Thenon-circular gear 103 engages with the non-circular gear fixed to thenut section 36b at the side of the secondary pulley 32. The circulargear 103 with the small gear 105a made as a spur gear or helical gearengaged at the reverse side of the circular gear 35c. A large gear 105bengaging with a small gear 106a which is formed on an intermediate shaft106 is fixed on an intermediate shaft 105. These gears compose areduction device 107 with high transmission efficiency. A comparativelysmall electric motor (or a supersonic motor) 109 is arranged with itsone side fixing to in the case 15. On an output shaft 109a of the motor109, a shaft 110 having a small gear 110a which engages the large gear106b arranged on the intermediate shaft 106 is fixed. A brake disc 111ais fixed on the shaft 110. An electromagnetic coil member 111b is fixedby a bolt to the case 15. The electromagnetic coil member 111b and thebrake disc 111a compose an electromagnetic brake 111 which restrains theoperating shaft 101. As the supersonic motor has a restraining mechanisminside, when it is being used, no special restraining mechanism, such asthe electromagnetic brake, is needed.

An assembly of the belt driven continuously variable transmission 30shall be explained in detail.

At the primary side, the thrust bearing 3a is arranged on the primaryshaft 30b and a stationary sheave 31a, the movable sheave 31b, thespring means 1, the thrust bearing 3b and an assembly the ball threaddevice 35 and the regulating retainer 4 are arranged on the shaft 30b;these are assembled in this order from the screw `i` side. Then a discspring 38, the movable race 34c and the roller 34b are enclosed in thehub section `a` and the fixed race 34a is screwed and stopped, whichcompletes the whole assembly. On the other hand, at the secondary side,are the thrust bearing 3c, the regulating retainer 8, the ball threaddevice 36, the movable sheave 32b and the stationary sheave 32a; theseare assembled in this order from the screw `t` side, thus the wholeassembly is completed.

In the sub assembly at the primary side, composed as the aboveexplanation, the belt 33 is held between both the sheaves 31a, 31b andthe hub section 2 of the stationary sheave 32a is inserted into theroller bearing 5e and the regulating retainer 4 is inserted into theshoulder 15b of the case 15 which is separable into two parts. At a subassembly on the secondary side, regulating retainer 8 is interposed inthe shoulder of the case 15, boss section of the movable sheave 32b isinterposed in the roller beraing 5b.

At this state, by the tolerances among each member the inital belttension is not correct and the stroke at the reversal of transmissiontorque of the regulating cam mechanism 34 is large. Therefore at thesecondary side, the regulating retainer 8 is rotated at the requiredmoment, the bolt section 36a integral with the retainer 8 is relativelyrotated against the nut section 36b and the spacing within the pulley 32is regulated. Then, the gear 7a of the regulating ring 7 is meshed withthe gear 8c of the retainer 8 and the ring 7 is fixed by the bolt B.While, at the primary side, a worm 4d is rotated to rotate theregulating retainer 4. The bolt section 35a is integral with theretainer 4. Though the bolt section 35a rotates integral with theretainer 4, as the bolt section 35a is axially positioned by the thrustbearing 3a, the nut section 35b moves axially to regulate the spacingwithin the pulley 31 correctly. By this process, the initial belttension is regulated to make the stroke of the pressure regulating cammechanism 34 correct and the position of both pulleys 31 and 32, or thebelt driving line is regulated to be correct.

If the worm 4d is operated from outside the case 15, regulation can bedone even after the case is assembled. And the worm 4d can be situatedat the secondary side or at both the secondary side and the primaryside. The regulating retainer can be situated at either the primary orthe secondary side.

The operation of this embodiment shall be explained below.

The rotation of the engine crank shaft is transmitted to the input shaft60 through the lock-up clutch CL or the fluid coupling 13 and thentransmitted to the sun gear 90S of the dual planetary gear device 90 andto the sleeve shaft 41. At the D range and the S range, the forwardclutch C1 connects and the reverse brake B2 releases, so that in thedual planetary gear device 90 the sun gear 90S and the carrier 90Crotate together and the positive rotation is transmitted from thecarrier 90C to the fixed race 34a of the pressure regulating cammechanism 34 of the belt driven continuously variable transmission 30.

The rotation of the fixed race 34a rotates the primary shaft 30bengaging with the thread `i` and also rotates the stationary sheave 31aof the primary pulley 31 through the roller 34b arranged on thewave-shaped surface, the movable race 34c and the spline 2a andfurthermore rotates the movable sheave 31b through the ball spline 6a.Both ends of the stationary sheave 31a are supported by the case 15through the bearings 5e and 5a. As spacing `c` is provided between thefixed race 34a and the hub section `a` and also between the movable race34c and the primary shaft 30b, the torque is not transmitted from thefixed race 34a and from the primary shaft 30b to the stationary sheave31a by friction. The whole torque transmitted from the carrier (theinput member) 90C is transmitted to the stationary sheave 31a throughthe pressure regulating cam mechanism 34. And at the pressure regulatingcam mechanism 34, the axial force corresponding to the input torquewhich works on the fixed race 34a works on the back surface of thesheave 31a through the disc spring 38. Regarding the sheave 31b, theball thread device 35 where the nut section 35b is connected to thesheave 31b is axially fixed to correspond to the shifting ratio,therefore the same strength of reaction force works on the back surfaceof the sheave 31b through the thrust bearing 3b. Accordingly the primarypulley 31 holds the belt 33 by the holding force corresponding to theinput torque. The axial force working on the movable sheave 31b works onthe flange section `k` of the primary shaft 30b through the thrustbearing 3b, the ball thread device 35, the regulating retainer 4 and thethrust bearing 3a. The axial force working on the stationary sheave 31aworks from the fixed race 34a to the shaft 30b through the thread `i`.Therefore the axial force is kept in the shaft 30b as tension force.Furthermore the rotation of the belt 33 is transmitted to the secondarypulley 32, and to the secondary shaft 30a through the key 6c and theball spline 6b.

At the belt transmission, the motor 109 is controlled based on thesignals from each sensor such as the opening ratio of the throttle andthe vehicle speed, etc. The operating shaft 101 is rotated through thereduction device 107. Then the nut section 35b at the side of theprimary pulley 31 is rotated through the circular gears 102 and 35c. Thenut section 36b at the side of the secondary pulley 32 is rotatedthrough the non-circular gears 103 and 36c. By this process, the nutsections 35b and 36b rotate relatively between the bolt section 35a and36a whose rotations are stopped by the case 15 at the regulatingretainer 4 and 8. The ball thread devices 35 and 36 move the movablesheaves 31b and 32b through the thrust bearings 3b and 3d, and theprimary pulley 31 and the secondary pulley 32 are set to the effectivediameter for the predetermined torque ratio. The electric current is cutwhen the torque ratio reaches the predetermined level, and theelectromagnetic brake 111 starts operating and keeps both the pulleys 31and 32 at the same torque ratio. At this state, both the ball threaddevices 35 and 36 linearly move. Therefore a difference arises betweenthe original traveling distance of the movable sheave by the belt 33 andthe traveling distance of the ball thread devices, however, thesecondary pulley 32 side rotates through non-circular gears 103 and 36c,the movable sheave is moved by the compensated traveling distanceaccording to the movable sheave.

In the case of the power transmission, as shown in FIG. 6, at thereduction range A of the belt driven continuously variable transmission30, the disc spring 1b contacts the retainer 1a and the spline 1btouches the retainer 1a and the spring means 1 generates pressing forceto the movable sheave 31b and the stationary sheave 31a in the directionof the belt pressing force. Besides the axial force based on thepressure regulating cam mechanism 34, a pressing force made by thespring means 1 works on the pulley 31. This pressing force is largest atthe most decelerating condition, the more the effective diameter of thebelt 33 becomes large, the more the pressing force gradually decreases.The disc spring 1b and the retainer at a certain shifting condition andthe only axial force to work on the pulley is the one based on thepressure regulating cam mechanism 34 shown in FIG. 5 (B range). The,break line shown in FIG. 6 shows the minimum belt pressing forcenecessary at the full-opening of throttle, or the whole torque-workingcondition. Considering the partly-working torque condition, or thedecrease of the axial force based on the pressure regulating cammechanism 34, the belt pressing force increased over the force of theminimum necessary in B range. By this motion, in range A where largebelt pressing force is required, the spring means 1 works, therefore thegenerated axial force based on the pressure regulating cam mechanism 34,even with its smaller measure compared to that of the conventional one,can be sufficient. Therefore, as shown in FIGS. 7 and 8, the generatedaxial force is lower than the conventional one, even when the force isin the decelerating range A or the other range B. However, based on theadditional force by the spring means 1 the belt pressing force of thisinvention is higher than the prior embodiment as shown in FIG. 9 in thedecelarating range A. And the difference of the belt pressing forcebetween this invention and the prior embodiment becomes smaller as thetransmitting torque becomes higher in the decelerating range A, as shownin FIG. 9, while the belt pressing force of the prior embodiment islarger than that of this invention and the difference becomes larger asthe transmission torque becomes higher in the decelerating range B.

Furthermore, the rotation of the secondary shaft 30a of the belt drivencontinuously variable transmission 30 is transmitted to the ring gear20R of the single planetary gear device 20 and also to the gear shaft70a through the carrier 20C.

And at the low-speed side L of D range, as shown in FIG. 3, as the lowone-way clutch F is in operating condition, the sun gear 20S receivesthe reaction force at the torque transmission from the ring gear 20R tothe carrier 20C. The rotation of this sun gear 20S is stopped by the lowone-way clutch F through a transfer device 80. The single planetary geardevice 20 works as a reduction mechanism. Therefore, the rotation of thesecondary shaft 30a of the belt driven continuously variabletransmission 30 is merely decelerated at the single planetary geardevice 20, then, through the reduction gear device 71 composed of a gear71a, 71c, an intermediate shaft 71b, the gear 71d and the mount gear72a, is transmitted to right and left front axle shafts 73l and 73rthrough the differential device 72.

When the throttle opening ratio and the vehicle speed reach certainlevels, the high clutch C2 receives signals from the controlling unit inorder to connect and get switched to the highspeed side. The rotation ofthe input shaft 60 is first transmitted to the belt driven continuouslyvariable transmission 30, then through the sleeve shaft 41 and the highclutch C2 transmitted to the sprocket 81 and finally to the sun gear 20Sof the single planetary gear device 20 through the silent chain 83 andthe sprocket 82. In this process, as the sprocket 81 at the input sideof the transfer device 80 receives the reaction force from the sun gear20S of the single planetary gear device 20 by the low one-way clutch F,a shift-shock caused by the shifting is prevented, the rotation startssmoothly by the connection of the high clutch C2 and the torque istransmitted to the sun gear 20S. By this process, the torque steplesslyshifted by the belt driven continuously variable transmission 30 and,the torque through transfer device 80 are combined at the singleplanetary gear device 20 and the combined torque is transmitted from thecarrier 20C to the gear shaft 70a. Furthermore, as the same with thelow-speed side, the combined torque is transmitted to the right and leftfront axle shafts 73l and 73r through the reduction gear device 71 andthe differential device 72.

As the low-speed side L of S range receives a negative torque made bythe engine brake and so on, the low-coast & reverse brake B1 engages andboth the forward and the reverse rotations of the sprocket 81 arestopped. The condition of the high-speed side H at S range is as thesame with that of the high-speed side of D range.

While, at the R range, the forward clutch C1 is released and the reversebrake B2 is engaged. Therefore, the rotation of the input shaft 60transmitted to the sun gear 90S of the dual planetary gear device 90 istransmitted as a reverse rotation, due to the suspension of the ringgear 90R, from the carrier 90C to the primary shaft 30b of the beltdriven continuously variable transmission 30. In this process, thereaction torque works on the sprocket 81 as the reverse rotation fromthe sun gear 20S of the single planetary gear device 20 through thetransfer device 80. Therefore the low-coast & reverse brake B1 operatesand the sprocket 81 is stopped.

An embodiment partially modified will be explained along with FIGS. 11and 12.

A spring means 1` of this embodiment has a coil spring 1'c in additionto multiple disc spring 1'b. The multiple disc spring 1'3b is screwedand stopped by a nap ring 1'd onto the outer surface of the boss section`b` of the stationary sheave 31a. A coil spring 1'c is arranged inseries between the disc spring 1'b and the shoulder n' of the movablesheave 31b through the retainer 1'a. And the coil spring 1'c iselastically weaker compared with the disc spring 1'b. Consequently, thefollowing situations are possible to set: to make the coil spring 1'cnatural length at the maximum effective diameter of the pulley 31 (referto the lower part of FIG. 11); to put the coil spring 1'c under acertain pressing condition; to make the coil spring 1'c under a certaindistance toward the retainer 1'a.

Therefore, in this embodiment, as shown in FIG. 12, with regard to thebelt pressing force, at A range, the disc spring 1'b having strongpressing force works, accordingly a large pressing force from the springmeans 1' is provided in addition to the axial force of the regulatingcam mechanism 34. Furthermore the more the shifting rates becomes small,the more the pressing force decreases with comparatively sharp decline.At a certain shifting range, the disc spring 1'b reaches its naturallength. At B range, the belt pressing force is a combination of the coilspring 1'chaving comparatively weak force and the axial force of theregulating cam mechanism 34, and the more the shifting ration becomessmall, the more the belt pressing force decreases with comparativelymoderate decline.

FEASIBILITY OF THE INDUSTRY

As has been explained, the belt driven continuously variabletransmission having a spring means, whose pressing force to hold thebelt decreases as the shifting ratio becomes smaller, can be feasible inany power transmission for transportation uses and industrial uses,especially in automatic continuously variable transmissions mounted inautomobiles.

We claim:
 1. A belt driven continuously variable transmissioncomprising:primary and secondary pulleys both of which have tworelatively slidable sheaves being supported on shafts, a pressureregulating mechanism for transmitting an axial force in accordance withthe transmission torque to at least one of said pulleys, actuatormechanisms for axially moving the movable sheaves of both pulleys, abelt wound around both pulleys, and spring means for biasing togetherthe sheaves of at least one of said pulleys with a force which isreduced as the shifting ratio is reduced.
 2. A belt driven continuouslyvariable transmission defined in claim 1, wherein said spring meansworks only within the range of high shifting ratio.
 3. A belt drivencontinuously variable transmission as defined in claim 2, wherein saidspring means is a plurality of multiple disc springs.
 4. A belt drivencontinuously variable transmission as defined in claim 1, wherein saidspring means includes plural springs which respectively have differentbiasing forces and natural lengths.
 5. A belt driven continuouslyvariable transmission as defined in claim 4, wherein said spring meansis a combination of at least one disc spring.
 6. A belt drivencontinuously variable transmission as defined in claim 1, wherein saidbelt driven continuously variable transmission which is used for anautomatic continuous variable transmission connects a secondary shaft ofsaid belt driven continuously variable transmission to a first rotatingelement of a planetary gear device; connects a second rotating elementof said planetary gear device, through a clutch, to an input shafttransmitting power to a primary shaft of said continuously variabletransmission; and connects a third rotating element of said planetarygear device to an output section; whereby power transmission isconducted exclusively through said belt driven continuously variabletransmission under the condition that said planetary gear device worksas a reduction mechanism by releasing said clutch and restraining saidsecond rotating element; and whereby, by engaging said clutch, saidplanetary gear mechanism works as a split drive mechanism to combinetorque transmitted through said belt driven continuously variabletransmission and torque transmitted from said input shaft to said secondrotating element.